In female rats a cyclic release of adenohypophyseal gonadotropins is initiated through neuroendocrine mechanisms involving a possible interplay of hypothalamic neurotransmitters, hypophysiotropic hormones, and steroids in addition to other as yet undetermined factors. It is the purpose of this research to investigate mechanisms by which these hypothalamic elements interact to initiate and relay synaptic impulses from the medial preoptic area (MPOA) to the median eminence secretory cells. The basal diencephalon of proestrous rats will be exposed and two cannulae inserted into the third ventricle to establish a push-pull flow of artificial CSF containing various test drugs. This method of drug administration permits exposure of only periventricular hypothalamic tissue. The ability of drugs in the perfusate to alter gonadotropin secretion patterns following electrochemical stimulation of the MPOA will correlated with changes in the subcellular distribution of neurotransmitters and hypophysiotropic hormones. These experiments should describe neurotransmitter environments which are conducive to or inhibitory to hypothalamic neurosecretion. In the second major facet of this research, neurotransmitter interactions that formulate to the gonadotropin surge will be investigated. Lateral ventricle to cisterna magna perfusions in consicious proestrous rats will be employed. Perfusates of various test agents to modify biogenic amine and indole amine activities will be exposed to periventricular tissue in morning proestrous rats or during the critical period to establish which transmitters are responsible for inhibiting or advancing the ovulatory surge.